<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style>
        .container {
            display: flex;
            justify-content: center;     /* 水平居中 */
            align-items: center;         /* 垂直居中 */
            height: 100vh;               /* 容器高度占满整个视口 */
        }

        .card {
            width: 200px;
            height: 200px;
            background: lightblue;
            text-align: center;
            line-height: 200px;
        }
    </style>
</head>
<body>
<div class="container">
    <div>
        <a class="card" href="#">你好！</a>
    </div>
</div>
</body>
</html>